1. Field of the Invention
The invention relates to an AC motor driving circuit for driving an AC motor by using an AC generator and a DC power source including a storage battery and a capacitor, and to an electric vehicle driving circuit using the AC motor driving circuit.
2. Description of the Related Art
For an AC motor driving circuit of this kind, there is previously known a circuit as shown in FIG. 11(see JP-A-2004-112883, for example). FIG. 11 is a circuit diagram showing a first example of a related AC motor driving circuit. In the circuit, a three-phase AC output of an AC generator M2 is converted to a DC output by a voltage source rectifier circuit 31 formed of a bridge circuit with a switching device and a diode connected in inverse parallel therewith as each of six arms. The DC output is smoothed by a capacitor 13 connected at a DC link (connection points N1 and N2). The smoothed DC output is transferred to a battery B from the DC link, to which the DC output from the battery B also is inputted. Moreover, between the DC link and the battery B, a DC chopper 12, formed of a reactor L1 and switching devices Q1 and Q2 paired with their respective corresponding diodes D1 and D26, is provided for carrying out DC voltage conversion for supplying DC electric power from the DC link to the battery B, and conversely, supplying DC electric power from the battery B to the DC link. Furthermore, the above DC electric power inputted to the DC link is converted to AC output by a voltage source inverter 14 formed of a bridge circuit with each of switching devices Q3 to Q8 paired with their respective corresponding diodes D3 to D8 connected in inverse parallel therewith as each of six arms. With the converted AC electric power, an AC motor M1 is driven. A control apparatus 30 controls the AC motor driving circuit based on torque instruction values (TR1 and TR2) and motor rotation numbers (MRN1 and MRN2).
An example of a circuit that directly converts an output of an AC generator to an AC output with a different frequency and feeds the converted output to an AC motor, a circuit shown in FIG. 12 is also known (see JP-A-2005-318731, for example). FIG. 12 is a circuit diagram showing a second example of a related AC motor driving circuit. In the circuit, an electric power conversion between motor-generators MG1 and MG2 is actualized with the use of a matrix converter 38, which is composed of nine switches arranged as a three by three switch matrix (switches SAa to SCc). Moreover, for exchanging electric power between a battery 12 and the motor-generators MG1 and MG2, a voltage source inverter 36 and a DC chopper 32 are provided. The voltage source inverter 36 is formed of a bridge circuit with each of switching devices Q31 to Q36 paired with their respective corresponding diodes D31 to D36 connected in inverse parallel therewith as each of six arms. The six arms are composed of two U-phase bridge arms 36U, two V-phase bridge arms 36V, and two W-phase bridge arms 36W. The DC chopper 32 is formed of a reactor L and switching devices Q11 and Q12 paired with their respective corresponding diodes D11 and D12. A control apparatus 40 controls the AC motor driving circuit based on control signal from a controller 48.
In the circuit shown in FIG. 11, the capacitor 13 for smoothing the DC output is required to have a large capacitance, which makes downsizing of the circuit difficult. Moreover, the reactor L1 is required in the DC chopper 12. In this respect, there is also a problem of enlarging the circuit. Furthermore, in the circuit shown in FIG. 12, a large DC capacitor C2 is also required between the battery 12 and the motor-generator MG2, which again makes downsizing of the circuit difficult. Moreover, the reactor L is required in the DC chopper 32. In this respect, again there is a problem of enlarging the circuit.
Furthermore, it is known that a combination of a current source rectifier and a voltage source inverter is used in a system called an indirect matrix converter, which is disclosed in the publication “Technical Trends of Direct AC/AC Converters”, IEEEJ Transactions on Industry Applications, vol. 126-D, No. 9, pp. 1161-1170, September 2006 (in Japanese). This publication describes the use of a current source rectifier and a voltage source inverter to allow large-sized parts such as the capacitor 13 shown in FIG. 11 to be omitted.
Accordingly, it is an object of the invention to eliminate the need for a DC capacitor and a reactor in a DC chopper from an AC motor driving circuit such as the above and to downsize the driving circuit.